Earlier this month, the promoter of the Isle of Wight festival had a go at Lily Allen. Miffed that Allen had cancelled her appearance at this year's event, John Giddings said: "I think the poor girl has got a few problems. Unfortunately, England, although it produces good girl singer-songwriters, they don't seem to be capable of running the course. These artists don't seem to have a responsibility to their audience." And he had a few choice words for Morrissey, who pulled out of the festival three years ago: "[He] claimed he was never booked and he told us he didn't have a drummer.

I offered him Phil Collins, and he still said he wouldn't do it."

Giddings pointed to the one thing Allen and Morrissey have in common - their Englishness - to explain their flakiness. Unfair as that might seem (Morrissey was never going to be swayed by the offer of Phil Collins, and it's far too early in Allen's career to judge her ability to "run the course"), Giddings was only voicing a very common presumption, both here and abroad, that British artists are shambolic and slapdash. When you compare them to the more successful American acts - ultra-professional, can-do - this attitude is even more pronounced.

If you were to devise a rule of thumb for distinguishing between British and American bands, the Brits will be the ones behaving as if everything were a bit of a joke, while the Americans will be checking the midweek chart on their BlackBerrys. At last month's Brit awards, Arctic Monkeys, who won awards for best group and best album, showed their gratitude by knocking the students of the Brit performing arts school, who were standing in the audience in front of them. The Mercury award-winning Damon "Badly Drawn Boy" Gough is famous for an on-stage style that ranges from the amateurish to the completely ramshackle, while hotly tipped band Foals recently told a BBC interviewer that they don't know how to play chords.

For my money, this is what makes British music great. It's irresponsible, innovative, quirky, piss-taking, unique, brilliant. Of course, there are exceptions - the more successful a band gets, the more likely they are to lose their quirkiness and acquire the discipline and drive that characterises so many American artists. So Coldplay and James Blunt are unlikely to cancel at short notice - but they make music as if they were service providers, and their fans clients. Where's the fun in that?

I grew up in New Jersey, so I have firsthand exposure to the American way of making music. In the US, it's always been a point of pride for even local bands to excel at playing their instruments; the British concept of inspired amateurishness would be laughed out of town. Professionalism was the goal, and everything else - cynicism, irreverence, a coherent fashion sense (all qualities that come as standard over here) - was an afterthought. Talk about dull. Even now that the internet has changed the mindset of younger US groups, with alternative bands such as Tilly and the Wall and Clap Your Hands Say Yeah realising that it's OK to be a mess so long as you're an interesting mess, they still lack the spark that underpins your typical UK act.

American critic Scott Plagenhoef, of the influential US music site Pitchfork, agrees. "There's a basic difference in values between American and English artists," he says. "The DIY aesthetic is more inclusive in the UK: 'We're on stage, why don't you get on stage, too?' A lot of British people think they can just do it. In the US, we're more suspicious if it looks too easy."

It was this inclusive British aesthetic that spawned punk in the 70s, indie in the 80s, dance music in the 90s and art rock in the 00s; it keeps the UK music scene overflowing with ideas. Tahita Bulmer, frontwoman of New Young Pony Club, tells me she thinks this creativity comes from not believing the hype. "American bands can press the flesh and do the meet-and-greets, and not feel like they're losing any sense of self," she says. "Whereas British bands are bound up in that English ideal about authenticity and not blowing their own trumpet. That makes them feel uncomfortable with hype and take the piss out of it." Hence the Monkeys turning up to the Brits dressed as farmers. It wouldn't happen in America, and that's America's loss.

Musician-turned-writer Sid Griffin has worked on both sides of the Atlantic, fronting California country-rockers the Long Ryders before moving to London in the 90s. "American bands come to Europe to tour and they're thrilled to be here," he says. "But they're also on time and shake hands and try to do gigs professionally, in the hope of being able to come back and build on it. Young English bands would just be partying and partying. But the Brits' ideas are better. It's about innovation over here. You have ideas to spare here, and in America we adhere to tradition." After 16 years in London, he has come to admire the way things are done here. "English bands know from the beginning how they're going to sound and look - it's discussed before the first rehearsal."

Not every artist with a UK passport has been touched by brilliance - but in my experience you're more likely to find something worth cherishing among the British mix of passion and self-deprecating insouciance.

I, for one, would rather a shambles - even a Babyshambles - over professionalism every time.